This invention relates to a crawler type drive apparatus which is suitable for application as a vehicular base carrier for various crawler type construction machines such as hydraulic power shovels, hydraulic cranes and the like.
Normally, construction machines such as hydraulic power shovels and hydraulic cranes, which are required to run on rough and muddy terrains of construction sites are equipped with a crawler type drive apparatus.
Crawler type drive apparatus of this sort generally include a truck frame having a pair of side frames at the opposite lateral sides of a center frame, front and rear brackets provided at the front and rear ends of each side frame for supporting thereon a drive sprocket and an idler wheel or vice versa, and a crawler belt wrapped between and around the drive sprocket and idler wheel. Upon rotationally driving the drive sprocket, the crawler belt, which is meshed with the drive sprocket, is driven by the drive sprocket to turn over around the drive sprocket and idler wheel via guide rollers, which are provided between the drive sprocket and idler wheels, putting the base carrier of a vehicle in travel.
In this connection, it has been well known in the art that, when put in travel, the vehicular base carrier with crawlers of this sort generates loud percussive or striking noises as crawler belts are turned around between the drive sprocket and idler wheel. These noises can be largely classified into intermittent striking noises and continuous striking sounds. Of these two kinds of noises, the intermittent percussive noises are attributable to undulatory vibrations which occur to each crawler belt which is turning around between the drive sprocket and upper rollers, causing the crawler belt to hit itself intermittently against the drive sprocket and idler wheel. On the other hand, the continuous striking noises are produced by a large number of crawler belt links as they are successively taken up onto the drive sprockets and meshed therewith in a polygonally bent shape.
In this regard, Japanese Laid-Open Utility Model Application 55-127678, 63-182981 and 6-6182 disclose crawler type vehicular drive apparatus employing guide roller bodies which are arranged to support lower side of a crawler belt between an upper roller and a drive sprocket. According to the crawler type drive apparatus described in these publications, by the provision of guide rollers which support lower side of a crawler belt, it becomes possible to suppress undulatory vibrations of the crawler belt between the upper roller and drive sprocket and thereby to minimize the intermittent striking noises as would be generated at a louder level by the undulatory vibrations.
However, although the crawler type drive apparatus of the above-mentioned prior art can reduce the intermittent striking noises as caused by undulatory vibrations of the crawler belt, there still remains the problem of continuous percussive or striking noises which are generated by the respective links of crawler belts when they are successively taken up onto the drive sprocket in a polygonally bent shape as mentioned hereinbefore.
Here, a reference is had to FIG. 11 to explain the reason why continuous striking noises are produced by a crawler belt when it is taken up onto a drive sprocket.
In FIG. 11, indicated at 1 is a drive sprocket, and at 2 a crawler belt which is passed around the drive sprocket 1 and an idler wheel (not shown). The crawler belt 2 is formed by successively connecting a plural number of links 3 pivotally by the use of connecting pins 4, which are each fitted with a bush 5. As the drive sprocket 1 is put in rotation in the direction of arrow A, the bushes 5 on the crawler belt 2 are successively meshed with the drive sprocket 1 as the links 3 are taken up onto the drive sprocket 1 progressively from time point T1 to T5.
In this instance, the links 3 are taken up onto the drive sprocket 1 in a polygonally bent shape, so that the bushes 5 are moved in the arrowed direction along a locus of movement as indicated by a curve B. At this time, a straight line C which is drawn through the centers of the bushes 5 at time points T2 and T4 lies on a line C which is tangential of pitch circle P of the drive sprocket 1. On the other hand, a straight line C' which is drawn through the centers of the bushes 5 at time points T1, T3 and T5 is downwardly deviated from the tangential line C by a deviational displacement D.
As a consequence, a bush 5 which is coming into meshing engagement with the drive sprocket 1 at time point T3 is vertically displaced by the deviational displacement D during movement from time point T2 to T3 and violently hit against the drive sprocket 1. It is considered that this phenomenon is repeated when the links 3 are successively taken up onto the drive sprocket 1, thereby producing continuous or repeated striking noises.
In this regard, attempts have been made to reduce such continuous striking noises which occur when crawler belt links are successively taken up onto a drive sprocket in a polygonally bent shape, for example, as disclosed in Japanese Laid-Open Utility Model Application 4-100973 and 50-133635, which disclose crawler belt type drive apparatus employing a crawler belt support structure between an upper guide roller and a drive sprocket in such a way as to support a crawler belt from beneath.
However, in the case of the above-mentioned Laid-Open Utility Model Application 4-100973, the crawler belt support is constituted by a truck frame boss which is provided on a truck frame in a position between an upper guide roller and a drive sprocket, a support bracket member which is erected on the truck frame boss, and a guide roller body which is supported on the support bracket member for rotation about a horizontal axis. Therefore, the crawler belt support requires a large number of parts, which will be naturally reflected by an increased production cost of the crawler type drive apparatus as a whole and also by a higher frequency of replacements of worn-out guide roller body, which is a quite troublesome job.
On the other hand, the crawler belt support according to the above-mentioned Japanese Laid-Open Utility Model Application 50-133635 is constituted by a support bracket member erected on a truck frame, an elongated holder plate securely fixed on the support bracket member and extended to hang over on the side of a drive sprocket, and an elongated slide plate fixedly mounted on the holder plate through a buffer material. In this case, the crawler belt support is also made up of a large number of parts and, additionally, bulky in size to such a degree as will necessarily result in higher production cost of the crawler type drive apparatus as a whole.
Besides, the slide plate which constitutes part of the crawler belt support is located in a position relatively distant from a meshing position where the crawler belt comes into meshing engagement with the drive sprocket, so that it fails to suppress sufficiently the continues striking noises which occur when the crawler belt is taken up onto the drive sprocket for meshing engagement therewith.
Here, reference is had to FIG. 12 to explain the reasons why continuous striking noises are generated by the crawler belt and drive sprocket in a louder level are explained, in case a slide plate of a crawler belt support structure is located at a distant position from the drive sprocket as in the above-mentioned Japanese Laid-Open Utility Model Application 50-133635.
In FIG. 12, denoted at 6 is a drive sprocket, at 7 an upper roller, and at 8 a crawler belt. This figure shows how the meshing point of the crawler belt 8 with the drive sprocket 6 changes when the position of the crawler belt 8 is shifted between the drive sprocket 6 and the upper roller 7.
In this instance, when a crawler belt support is located in a position which is spaced from the rotational axis E of the drive sprocket 6 by a distance F1, the crawler belt 8 and drive sprocket 6 are meshed with each other from position H1 to position H1'. However, it is to be noted that the initial meshing position H1 is deviated to a lower position by a displacement K1 from a tangential line J which connects the drive sprocket 6 and the upper roller 7. Further, in case a crawler belt support is located in a position G2 which is spaced from the rotational axis E by a distance F2, the crawler belt 8 and drive sprocket 6 are meshed with each other from position H2 to position H2'. In this case, the meshing position H2 is deviated downward of the tangential line J by a displacement K2. Furthermore, in case a crawler belt holder is located at a position G3 which is spaced from the rotational axis E by a distance F3, the crawler belt 8 and drive sprocket 6 are meshed with each other from position H3 to position H3'. In this case, the meshing position H3 is deviated downward of the tangential line J by a displacement K3.
In this manner, the displacement K of the meshing position H of the crawler belt 8 and drive sprocket 6 from the tangential line J becomes larger with increases in the distance of the location G of the crawler belt support from the drive sprocket 6. The greater the displacement K, the greater becomes the energy necessary for the drive sprocket 6 to kick up the crawler belt 8 at the time of meshing engagement therewith. Namely, the louder continuous striking noises are produced by meshing engagement of the crawler belt 8 and the drive sprocket 6.
Accordingly, it is desirable to locate the crawler belt support as closely to the drive sprocket as possible and in such a way that the crawler belt 8 is taken up onto the drive sprocket 6 from a tangential direction. Nevertheless, the above-described prior art crawler belt support is located in a distant position from the drive sprocket, failing to suppress to a satisfactory degree the continues striking noises as occurring when the crawler belt is continuously meshed with the drive sprocket.
In view of the problems inherent to the prior art as discussed above, it is an object of the present invention to provide a crawler type drive apparatus which can securely suppress continuous percussive or striking noises as would be generated by a crawler belt when taken up onto a drive sprocket in a polygonally bent shape, and which is simplified in construction.